Create a NAT to subnet

This is my first time operating the Fortigate Firewall (100F) and I need to create a configuration of NAT that allows me to avoid many policies for each server that I have to NAT traffic. For example, I have a subnet 172.16.5.0/24 and I need to allow each server to reach another two servers over the VPN tunnel in a bidirectional way. What is the best way to do that?